Electrical fuel level sensors typically use a float arm arrangement to measure the level of fuel in a tank. While the float arm arrangement is simple and generally effective, it does have some properties which create issues in certain applications.
As a first issue, a fuel tank with a float arm sensor must provide a volume of space through which the float arm swings as the fuel level varies. This need for volume places a design limitation on the shape of the fuel tank. Since a fuel tank is generally a large object mounted within a vehicle, the volume of space needed for a swing arm may be in contention with space needed to satisfy other goals. These other goals may include, by way of example, aesthetic styling of the vehicle or space needed to engineer for crash worthiness.
As a second issue, a float arm generally has several moving parts. These parts include a float pivotally mounted to one end of a float arm. The other end of the float arm is typically attached to a potentiometer or array of switched resistive pads. The float arm moving up and down causes an electrical wiper to sweep across a resistive element of the potentiometer or array of switched resistive pads, thereby electrically indicating the level of fuel in the tank. Among these moving parts, there is the possibility of binding between them. There is also the possibility of the fuel, or additives thereto, chemically deteriorating the potentiometer or array of switched resistive pads, thereby causing an erroneous fuel level indication.